Battery Emf, Chemistry, and Internal Resistance

All flashcards

What is electromotive force?

Emf is the energy or work supplied by a source per unit charge. It is represented by $\varepsilon$ and measured in volts.

Why is emf measured in volts?

Emf is energy per charge, and $1\ \text{V} = 1\ \text{J/C}$.

What does it mean to call a battery a charge pump?

The battery uses internal energy, usually chemical energy, to move charge against the electrical influence inside the source and maintain separated charge at its terminals.

How do conventional current and electron flow differ in a metal wire?

Conventional current is defined in the direction positive charge would flow. Electrons, which carry negative charge, move in the opposite direction.

How does an ideal battery differ from a real battery?

An ideal battery has no internal resistance and maintains terminal voltage equal to its emf. A real battery has internal resistance, which can affect its terminal voltage when current flows.

Quiz questions

1. A real source with emf $\varepsilon$, internal resistance $r$, and load resistance $R$ is connected in series. What is the circuit current?Answer: $I=\frac{\varepsilon}{R+r}$
2. A source with emf $\varepsilon$ and internal resistance $r$ supplies current $I$. What is its terminal voltage?Answer: $V_{\text{terminal}}=\varepsilon-Ir$
3. What principle do lead-acid and lithium-ion batteries share despite using different materials?Answer: Chemical processes maintain charge separation and a potential difference.
4. What does a battery tester assess when it connects a small load to a battery?Answer: Whether terminal voltage remains adequate while current is drawn.
5. With current defined as positive when leaving a battery's positive terminal, what happens during charging?Answer: Current is negative, and terminal voltage exceeds the emf.